The present invention relates to a technique of constructing a boron phosphide-based semiconductor device utilizing a high-resistance boron phosphide (BP)-based semiconductor which is effective in evading unnecessary leakage or passing of a device operating current.
As the Group III-V compound semiconductor comprising boron (B) belonging to Group III of the Periodic Table and an element belonging to Group V, boron phosphide (BP) is known (see, Nature, 179, No. 4569, page 1075 (1957)). For the boron phosphide, various band gaps have been heretofore reported. For example, B. Stone et al. report a room temperature band gap of about 6 electron volt (eV) for polycrystalline BP film (see, Phys. Rev. Left., Vol. 4, No. 6, pages 282 to 284 (1960)). Furthermore, Manca reports a band gap of 4.2 eV (see, J. Phys. Chem. Solids, 20, page 268 (1961)). However, a value of about 2 eV has been heretofore commonly employed as the band gap of boron phosphide (see, (1) RCA Review, 25, pages 159 to 167 (1964), (2) Z. anorg. allg. chem., 349, pages 151 to 157 (1967), (3) Iwao Teramoto, Handotai Device Gairon (Outline of Semiconductor Device), 1st ed., page 28, Baifukan (Mar. 30, 1995)).
On the other hand, boron phosphide has a small ionic bonding degree according to Philips of 0.006 (see, Philips, Handotai Ketsugoron (Semiconductor Bonding Theory), 3rd imp., pages 49 to 51, Yoshioka Shoten (Jul. 25, 1985)) and therefore, is characterized in that a conductive semiconductor layer is readily obtained (see, JP-A-2-288388 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)). Because of this, a case of using an electrically conducting BP layer as a current narrowing layer constituting a Group III nitride semiconductor laser diode (LD) is heretofore known (see, JP-A-10-242569). In a light-emitting diode (LED), the BP layer is used, for example, as a buffer layer on a single crystal substrate (see, JP-A-2-275682). On the other hand, effective electron mass of electron boron phoshipde is relatively large (see, JP-A-10-242569, supra) and therefore, it is considered that an n-type low-resistance BP crystal cannot be so readily obtained (see, JP-A-2-288388, supra).
When reviewed from the aspect of crystallographic property, boron phosphide of cubic spharelite type (see, Philips, Handotai Ketsugoron (Semiconductor Bonding Theory), 3rd imp., pages 14 and 15, Yoshioka Shoten (Jul. 25, 1985)) has a lattice constant of 4.538 xc3x85 which is almost the same as that of cubic gallium nitride (c-GaN: lattice constant=4.510 xc3x85). The distance between {110} lattice planes of BP is about 3.209 xc3x85 and this is almost equal to the a-axis lattice constant of hexagonal GaN (h-GaN), namely, 3.180 xc3x85 (see, Handotai Device Gairon (Outline of Semiconductor Device), page 28, supra). By making use of this good lattice matching, a Schottky junction field effect transistor (MESFET) has been heretofore constructed by utilizing a junction structure of a BP buffer layer and a GaN crystal layer (see, JP-A-2000-31164).
The boron phosphide (BP) is an indirect transition-type semiconductor (see, Handotai Device Gairon (Outline of Semiconductor Device), page 28, supra). In the indirect transition-type semiconductor, the radiation recombination efficiency of a carrier in emitting light is low as compared with a direct transition-type semiconductor (see, K. Seeger, Semiconductor no Butsuri Gaku (Ge) (Physics of Semiconductor (Last Volume))xe2x80x9d, 1st imp., page 392, Yoshioka Shoten (Jun. 25, 1991)). Because of this, boron phosphide, which is an indirect transition-type semiconductor, is used, for example, as a current narrowing layer as described above but not as a light-emitting layer (active layer) of an LED or LD. In a field effect-type transistor, use of BP as a buffer layer has been proposed.
For example, in the case of a buffer layer for use in a field effect transistor, the buffer layer must be constituted by a high-resistance crystal layer so as to prevent the leakage of drain current. However, the band gap at room temperature of conventional boron phosphide is as low as about 2 eV (see, (1) RCA Review and (2) Z. anorg. allg. chem.) and moreover, the crystal has a low ionic bonding property and is readily made conductive. Therefore, conventional techniques have a problem in that a high-resistance buffer layer suitable for use in MESFET cannot be readily obtained.
Also, a technique of manufacturing a super lattice structure of boron phosphide having a band gap of 2 eV with an aluminum nitride (AIN)-based mixed crystal to obtain a structure having a band gap of 2 eV or more at room temperature has heretofore been disclosed (see, JP-A-2-275682, supra). However, this conventional technique has a problem in that cumbersome means is necessary for forming the super lattice structure.
The present invention has been made to overcome the above-described problems in conventional techniques. Therefore, an object of the present invention is to form a high-resistance boron phosphide-based semiconductor layer without requiring any cumbersome means as in conventional techniques and to provide a boron phosphide-based semiconductor device constructed by using this high-resistance boron phosphide-based semiconductor layer. The object of the present invention includes providing a production method of the boron phosphide-based semiconductor device.